1. Field of the Invention
The present invention relates to pipettor heads generally and, more particularly, but not by way of limitation, to a novel pipettor head and method of use in which each of the aspiration/dispensing needles therein is connected to an open top standpipe the top of which is disposed in a vacuum/pressure chamber to which vacuum or pressure may be selectively applied. A method of using the pipettor head is also provided.
2. Background Art
The pipettor head of the present invention may be used, for example, in the Quadra product line furnished by Tomtec Inc., of Hamden, Conn.
In the field of drug discovery for life science, there is a need for dispensing small aliquots of various reagents and biological materials. As the volume of testing increases, economics demands doing more with less. Scientific efforts have reduced the quantities of assay reagents required from milliliter quantities down to microliter quantities and lower. Instrumentation is required to maintain the required levels of accuracy and precision at these levels.
A wide variety of fluid delivery systems are in use. They include air displacement and positive displacement pipettor systems, single channel and multiple channels. In the nanoliter volume ranges, time/pressure systems using inkjet technology have found applications. This invention relates to this type of technology. A time pressure system simply opens a passageway allowing it to flow from a period of time. Controlling the open time combined with the head pressure, the volume dispensed can be controlled. Ink jet printing uses a fast acting, electronically activated, solenoid valve to open and close the flow path very quickly. A head pressure is applied to the flow path, which has a small orifice at the output end to create the backpressure required. If the head pressure is high enough to provide sufficient kinetic energy at the outlet orifice to overcome surface tension forces, small aliquots of liquid can be ejected in a non-contact mode. This is the principle of ink jet printing.
In ink jet printing, a common fluid, i.e. ink, is ejected. In the life science arena, multiple liquids must be transferred. This requires aspirating and dispensing. This can be accomplished by applying a negative pressure (vacuum source) instead of a positive pressure on the side of the valve opposite the orifice. This vacuum will cause liquid to move from the immersed orifice into a reservoir. Applying a positive pressure to the reservoir now reverses the direction of controlled flow. This type of technology is currently in use.
The conventional inkjet system, used for aspirating and dispensing, has a closed reservoir on one side of the fast acting solenoid valve and a small output orifice on the opposite side. Opening the valve, with the orifice immersed and a vacuum applied to the reservoir, will cause aspiration of the liquid into the reservoir. Closing the ink jet solenoid valve and applying positive pressure to the reservoir will reverse the action. This creates a dispense from the reservoir when the valve opens again.
In applications, such as life science, the reagents to be transferred are precious. Therefore dead volume, i.e. volume used to fill but cannot be used, is of concern. This requires the reservoir to be small in contained volume.
If multiple reagents are to be dispensed from the same flow path, there needs to be means of washing the flow path between reagents to prevent cross contamination. Commonly this is accomplished with multiple aspirating and dispensing functions with a suitable wash fluid. Due to the small dead volume requirement of the closed reservoir, many repetitive aspirate/dispense functions are required. In many applications it requires appreciably more time to rinse the flow passages than the productive time.
Another impediment, with washing in this mode, is clogging of the ink jet solenoid valve due to particulate matter in the fluid stream. On the dispense function, particulate matter from the reservoir must pass down through the valve seat which is a very confined space. As the valve armature closes on the valve seat, any particulate matter on the valve seat is hammered into the sealing surface of the seat. This leads to premature system failure.
Accordingly, it is a principal object of the present invention to provide a pipettor head and method of use for transferring small aliquots of liquid, typically from 50 nanoliters to 5 microliters (although not limited to these volumes) from a source to a destination.
A further object of the invention is to provide such a pipettor head and method of use that minimizes dead volume.
Another object of the invention is to provide such a pipettor head and method of use that requires minimal rinsing time vs. pipetting time.
An additional object of the invention is to provide such a pipettor head that is adaptable to single or multiple channel functions.
Yet a further object of the invention is to provide such a pipettor head and method of use that provides a rinsing function that prolongs the life of the valve which is the active component of the pipettor head.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.